In the case of a cold front,
a colder, denser air mass lifts the
warm, moist air ahead of it. As the air rises, it cools and its moisture
condenses to produce clouds and precipitation.
Due to the steep slope of a cold front,
vigorous rising motion is often produced,
leading to the development of
showers and occasionally severe
thunderstorms.

In the case of a warm front,
the warm, less dense air rises up and over the colder
air ahead of the front. Again, the air cools as it rises
and its moisture condenses to produce clouds
and precipitation.
Warm fronts have a gentler slope and
generally move more slowly than cold fronts, so the
rising motion along warm fronts is much more gradual.
Precipitation that develops
in advance of a surface warm front is typically
steady and more widespread than precipitation associated with a
cold front.